This invention relates to an apparatus for controlling a continuously variable transmission for use with an automotive vehicle to change the engine brake force when the vehicle is coasting.
Some automotive vehicles employ a continuously variable transmission having an input shaft coupled to the engine and an output shaft coupled to the drive shaft for transmitting a drive from the engine to the drive shaft. Such a continuously variable transmission operates with a speed ratio controlled in a manner to bring the speed of rotation of the input shaft into coincidence with a target value calculated as a function of engine throttle position (or accelerator pedal position) and vehicle speed. It is the current practice to decrease the target input shaft speed value as the throttle position decreases. If the vehicle is coasting on a downhill slope, the operator will release the accelerator pedal. This causes the throttle position to decrease so that the target input shaft speed value is changed (decreased) in a direction to weaken the engine brake. As a result, the operator would feel an excessive degree of vehicle acceleration in spite of the fact that the accelerator pedal is released and increase the frequency at which the operator depresses the brake pedal.
For example, Japanese Patent Kokai No. 6-81932 discloses a continuously variable transmission control apparatus intended to reduce the frequency at which the operator depresses the brake pedal when the vehicle is coasting on a downhill slope by increasing the lower limit for the target input shaft speed value as the absolute value of the vehicle weight gradient resistance increases to perform aggressive operate engine brake operations. With such a conventional apparatus, however, the target input shaft speed value changes frequently to provide a sense of incompatibility to the operator with changes in the gradient of the slope.
It is a main object of the invention to provide an improved continuously variable transmission control which can provide a smooth engine brake force change to meet the operator""s expectation therefor when the vehicle is coasting with the accelerator pedal being released.
There is provided, in accordance with the invention, an apparatus for controlling a continuously variable transmission for use with an automotive vehicle including an accelerator pedal. The transmission has an input and output shaft. The transmission is operable at a variable speed ratio for transmitting a drive from the input shaft to the output shaft. The continuously variable transmission control apparatus comprises means for sensing vehicle operating conditions including vehicle acceleration and vehicle speed, means for producing a released accelerator pedal indicative signal when the accelerator pedal is released, means for calculating a target value for the speed of rotation of the input shaft based on the sensed vehicle operating conditions, means for calculating a correction factor per predetermined unit time based on the sensed vehicle acceleration when the sensed vehicle acceleration exceeds a threshold value in the presence of the released accelerator pedal indicative signal, means for adding the correction factor to the target input shaft speed value to correct the target input shaft speed value in an increasing direction at intervals of the predetermined unit time, means for decreasing the threshold value as the vehicle speed increases, and means for controlling the speed ratio to bring the input shaft speed into coincidence with the corrected target value.
In another aspect of the invention, the continuously variable transmission control apparatus comprises means for sensing vehicle operating conditions including vehicle acceleration and vehicle speed, means for producing a released accelerator pedal indicative signal when the accelerator pedal is released, means for calculating a target value for the speed of rotation of the input shaft based on the sensed vehicle operating conditions, means for calculating a correction factor per predetermined unit time based on the sensed vehicle acceleration when the sensed vehicle acceleration is less than a threshold value in the presence of the released accelerator pedal indicative signal, means for subtracting the correction factor from the target input shaft speed value to correct the target input shaft speed value in a decreasing direction at intervals of the predetermined unit time, means for decreasing the threshold value as the vehicle speed increases, and means for controlling the speed ratio to bring the input shaft speed into coincidence with the corrected target value.
In another aspect of the invention, the continuously variable transmission control apparatus comprises means for sensing vehicle operating conditions including vehicle acceleration, means for producing a released accelerator pedal indicative signal when the accelerator pedal is released, means for producing a brake application indicative signal in response to application of braking to the vehicle, means for calculating a target value for the speed of rotation of the input shaft based on the sensed vehicle operating conditions, means for calculating a correction factor per predetermined unit time based on the sensed vehicle acceleration to bring the vehicle acceleration into a predetermined range in the presence of the released accelerator pedal indicative signal, means for adding the correction factor to the target input shaft speed value to correct the target input shaft speed value at intervals of the predetermined unit time, means for controlling the speed ratio to bring the input shaft speed into coincidence with the corrected target value, and means for retaining the correction factor in the presence of the brake application indicative signal.
In another aspect of the invention, the continuously variable transmission control apparatus comprises means for sensing vehicle operating conditions including vehicle acceleration, means for sensing an operator""s demand for vehicle cruising, means for sensing an operator""s demand for vehicle acceleration, means for calculating a target value for the speed of rotation of the input shaft based on the sensed vehicle operating conditions, means responsive to the sensed operator""s demand for vehicle cruising for correcting the calculated target input shaft speed value to bring the vehicle acceleration into a predetermined range, means responsive to the operator""s demand for vehicle acceleration sensed during the target input shaft speed value correction for changing the target input shaft speed value at a predetermined rate toward the calculated target value, and means for controlling the speed ratio to bring the input shaft speed into coincidence with the corrected target value.
In still another aspect of the invention, the continuously variable transmission control apparatus comprises means for sensing vehicle operating conditions including vehicle acceleration, means for sensing a degree to which the accelerator pedal is depressed, means for calculating a target value for the speed of rotation of the input shaft based on the sensed vehicle operating conditions, means for correcting the calculated target input shaft speed value to bring the vehicle acceleration into a predetermined range when the sensed degree indicates the accelerator pedal released, means for changing the target input shaft speed value at a predetermined rate toward the calculated target value when the sensed degree indicate the accelerator pedal depressed during the target input shaft speed value correction, and means for controlling the speed ratio to bring the input shaft speed into coincidence with the corrected target value.